This invention relates to hand bender tools for electrical conduit and similar pipes and tubes, and more particularly to a bending tool with sighting and angle indicators for determining the angle of bend of the piece being bent.
Conduit benders, or tube benders as they are known, are commonly used by electricians and others, mainly for bending conduit to run wires and cable through. Such a conduit bender is described, for example, in U.S. Pat. Nos. 4,009,602, Linquist; 4,442,695, Gardner; and 4,622,837, Bergman.
A typical tube bender comprises two parts: a handle and a head. The handle is screwed into the head and the head has an arcuate shoe at the bottom with a laterally concave groove in the bottom of the shoe into which the conduit fits with a small clearance. The head has a hook which is hooked around the conduit received in the groove and the conduit is bent by exerting a force on the handle to roll the shoe along the conduit, with the conduit between the floor and the shoe.
The arcuate bend imparted to the conduit or tubing as the tool head is rocked has a radius substantially equal to that of the arc to which the shoe is curved along its length. The bend angle produced in the conduit is dependent upon the distance through which the handle is swung rearward during the bending operation. The bend angle is the angle between the straight sections of conduit that are at opposite ends of the curve imparted to the conduit by means of the tool.
Without some means to accurately determine the bend angle, the user must estimate the necessary bend, see if the bend was correct by disengaging the tool, and then correct any error by increasing or decreasing the bend in the already bent piece. This procedure is time consuming and expensive in a work environment.
Various means and methods have been developed to provide an accurate determination of the bend angle while bending the conduit. Several methods such as disclosed in U.S. Pat. No. 5,669,258, Luebke, involve attaching a tube bend angle indicator to the tool handle. As the handle is moved to make the bend in the conduit, a pointer or other indicator (e.g., a bubble in a bubble level indicator) moves relative to horizontal to indicate the bend angle. This type of bend angle indicator provides a high degree of accuracy. However, such indicators are not integral parts of the bender and are not always available at a job site.
In U.S. Pat. Nos. 4,442,695, Gardner and 4,009,603, Linquist, markings on the tool head provide a sight line for determining the bend angle by the user. When markings on the tool head were properly aligned during the bend operation, the conduit was substantially bent to the desired bend angle. This type of bend angle indicator can be cast into the head and is less susceptible to damage in a harsh environment.
The invention disclosed in U.S. Pat. No. 4,442,695, Gardner, represented a significant improvement over the arrangement in U.S. Pat. No. 4,009,602, Linquist, in that a more accurate bend angle was obtainable on the job site. Both of these prior art inventions, however, were limited in the number of predetermined bend angles that could be displayed on the bender head. In the Linquist invention, available space for marking angles is limited to a small arc on the front end of the shoe. The Gardner invention solved this problem by providing angle indicators along the length of the shoe, but the upper rib segment of the indicator is crowded on the handle socket, converging on a single apex, thereby limiting the addition of additional angle indicator ribs. The limited number of predetermined bend angles requires the user to estimate bend angles that are not indicated on the tool. Therefore, it is desirable to provide a bending tool with the capability of indicating more predetermined bend angles, thus reducing the amount of estimating required.